The present invention generally relates to mechanical heart valve prostheses. More specifically, the present invention relates to mechanical heart valve prostheses having improved pivot designs.
Prosthetic valves are utilized to replace malformed, damaged, diseased or otherwise malfunctioning valves in body passageways, such as heart valves, including the tricuspid valve, the mitral valve, the aortic valve and the pulmonary valve. Such prosthetic heart valves are typically implanted into the heart either by open chest surgery which requires a sternotomy or by minimally invasive surgery which requires a thoracotomy between adjacent ribs.
Heart valve prostheses may be divided into two groups, namely, tissue valves and mechanical valves. Typically, prosthetic tissue valves are harvested from a suitable animal heart, usually a porcine heart, prepared according to known methods, and may be mounted to a stent to facilitate implantation. Tissue valves prepared from pericardial tissue are also known in the art. Mechanical valves, by contrast, utilize synthetic materials to form a valve having a ball, a disc, a pair of leaflets (bileaflet), or a plurality of leaflets to regulate blood flow therethrough.
A mechanical heart valve prosthesis is optimally designed to perform the same functions as a healthy native valve. In particular, a mechanical heart valve is designed to regulate blood flow into and out of the heart chambers. Mechanical heart valves permit blood flow in only one direction and are actuated between an open position and a closed position by the changing hemodynamic conditions of the heartxe2x80x94i.e., by changes in blood flow and pressure caused by the pumping action of the heart.
Ideally, a mechanical heart valve prosthesis imposes no more resistance to blood flow than a healthy native heart valve. However, mechanical valves typically have somewhat less efficient flow and may be more thrombogenic than healthy native valves. The inefficient flow may be caused by limitations associated with the design, such as the pivots, the profile or shape of the leaflets, and movement of the leaflets relative to the pivots. Such design limitations may cause disturbed flow such as excessive turbulence, high shear stress, flow separation, and recirculation to occur across the valve, which may increase the thrombogenic risk of the valve. Improvements in flow efficiency and thrombogenic resistance are desirable to more closely simulate a healthy native valve.
A particularly successful mechanical heart valve prosthesis design utilizes leaflets that are disposed in and pivotally attached to an annular housing. For each leaflet, there are two pivots that typically include a protrusion formed on the leaflet which is rotatably disposed in a recess formed in the housing. Such pivot assemblies may be susceptible to some degree of thrombus formation because blood flow may become disturbed and/or stagnant as it passes through the pivot.
To address the issue of thrombus formation, a standard practice among treating physicians is to provide anticoagulant therapy. The administration of anticoagulants reduces coagulation protein function and platelet aggregation which are precursors to thrombus formation. However, such anticoagulant therapy may lead to internal bleeding, which is undesirable. Therefore, it is desirable to reduce the probability of thrombus formation in another manner.
The present invention provides several pivot designs for mechanical heart valve prostheses that inherently reduce the probability of thrombus formation by minimizing the stagnation and disturbance of blood flow through the pivot assembly. The pivot designs of the present invention provide a depression or recess, preferably in the housing, that have a profile adapted to promote less disturbed and/or less stagnant blood flow.
In one aspect, the pivot depression or recess may have a smooth continuous surface free of surface protrusions or stopping walls to minimize flow disturbance and stagnation. A separate pair of stop protrusions for each leaflet may be disposed on the lumen surface of the housing to maintain the leaflets in the open and/or closed position if desired. Another embodiment includes providing curved profiles to the leaflets and valve body to reduce flow disturbances.
In one aspect, a pivot recess may have a central radius of curvature, an upstream radius of curvature and a downstream radius of curvature, wherein the radius of curvature varies therebetween in order to reduce blood flow disturbance and/or stagnation. In one aspect, a pivot recess may have a convex surface in addition to a concave surface in order to reduce the size of the recess and still minimize flow disturbance and/or stagnation.